Bluestone gravel turning white

We have bluestone gravel that is now becoming white. Every time it rains more and more pieces are becoming white. It appears to be painted. Is that possible?

It now has a salt and pepper appearance. Int is also a concerne that it may not be this might be good for my yard. We also are concerned about the fact that we have children and pets that may be exposed to it. The contractor has given a less than reassuring answer.